Historically fluid seals and rod wipers have been separate articles, since seals are designed for pressurized environments while rod wipers are directed to the exclusion of contaminants from piston rods and shafts. Combined fluid seals and rod wipers have been used in a piston rod environment to function as both a seal and as a dirt and contaminant excluders. Heretofore, these designs have suffered because when the seal is pressurized, the sealing action tended to distort the rod wiper.
Typically fluid seals are resident in an annular packing chamber or groove that is bounded by a piston rod on one side and a piston housing or cylinder which surrounds the rod. As a piston rod reciprocates or rotates about its own axis in a piston housing, lubrication fluids contact the seal and may be contained within the packing chamber. The function of the seal, in a low pressure environment, is to provide sealing ability due to the elastic interference or compression fit of the seal with the annular gland or groove in the packing chamber. This interference or compression fit of the seal with the annular groove walls may be measured in terms of the amount of deflection of the seal cross-section.
A prior art illustration of a fluid seal and rod wiper in combination is U.S. Pat. No. 3,921,991 to Beck. The Beck Patent discloses a u-shaped cross-sectional configuration for a ring-like member made from an elastomeric material such as polyurethane and other elastomeric materials, such as neoprene or natural rubber. The ring-like member D of FIG. 1 of Beck is a one piece elastomer having tails 28 of equal width, one of which acts to wipe a rod portion 16 and the other tail of the member D acting to press against the farthest axially-directed wall of the groove 18. Such a U-ring configuration member provides good relief volume and low compression force. Therefore, this one piece u-shaped cross-sectioned annular member D acts as a good rod wiper due to its ability to provide relief volume, while its sealing ability is limited. Additionally, compression setting (a failure of the seal and wiper to return to its pressure-free dimensions) is a factor that the Beck Patent does not account for.
A prior art attempt to improve on the single piece seal and wiper assembly is illustrated in the wiper assembly configuration shown in FIG. 11 of this application (a metal clad wiper manufactured under the trademark MICRODOT). FIG. 11 shows a seal and rod wiper assembly 60 made from two pieces, an elastomeric urethane material rod wiper 62 and a metal plate 64. Wiper arm 68, acting as a rod wiper, abuts the piston rod and shaft. Wiper arm 66 is molded and formed to accommodate the metal ring 64, which is molded and clamped into the arm 66 by the curved head 69 of the ring 64.
As the wiper 62 is subjected to wear and pressure and temperature changes, the wiper assembly 60 is more likely to walk out of its gland within the piston housing surrounding the shaft. The wiper arm 68 transmits side loading to the mold metal ring 64 and head 69 which can cause the rod wiper arm to move out of its groove. With molded rings in the seal, the seal can begin to wiggle and walk out of its seat in the groove. Such a molded configuration reduces the forces needed to remove the ring. A molded reinforcing ring embedded within the elastomeric seal can cause the seal assembly not to follow the rod uniformly, resulting in leakage of contained fluids while allowing dirt or other contaminants into the system.